The invention relates to a plant, a press and a control device for reducing the capillary-bound water content in fiber cells of carbon-containing, finely comminuted solid materials and/or sludge.
The object underlying the invention of German patent 1 95 35 315.3 is to make it possible, by means of a new method, to use raw brown coal on a large-scale industrial basis by means of a thermomechanical dewatering, in which the overall efficiency of the conversion in power plant processes is improved and in which the continuous throughput of large amounts of coal-containing solids required for this purpose is achieved. In order to avoid blow-off at the edges of the bulk material mat under the action of the steam pressure and to achieve a uniform distribution of thermal energy over the press surfaces without reducing the steam pressure at the edges, it was further intended to provide a technical solution for a plant and press which no longer contains, or which avoids, the disadvantages described.
In terms of the method, this object is achieved by the combination of the following process steps:
a) a starting material is used which at the beginning of the cycle, is vapor-blasted in a pressure chamber, which is sealed in an essentially steam-tight manner and has been preheated to above 100.degree. Celsius, and using a steam which has been superheated to .gtoreq.150.degree. Celsius,
b) the compacting pressure on the starting material is greater than the pressure prevailing in the starting material as a result of the bulk density, corresponding at most to approximately the steam pressure introduced of 5 bar to 8 bar, and, then
c) after having reached a temperature of about .gtoreq.125.degree. Celsius in the starting material, the injection of steam is terminated and, depending on the particle size of the starting material, a high mechanical, specific press pressure of up to at most 75 bar becomes effective, in order to effect reduction to a residual water content of up to 20 percent by weight.
The thermomechanical dewatering method as disclosed in German patent 1 95 35 315.3 makes it possible to dewater brown coal economically with a low consumption of thermal and mechanical energy. The overall efficiency of the power plant process for the conversion of brown coal with a high moisture content can be significantly improved by the upstream connection of the method in accordance with the invention for removing the water, which method is beneficial in terms of energy. Moreover, compared with the known thermal drying methods, the energy required to evaporate the water is cut down.
The solution in terms of the plant for carrying out the process steps disclosed in German patent 1 95 35 315.3 consists in guiding a revolving scattering belt through a pressure chamber which is integrated in a single-daylight press and in opening and closing this pressure chamber by means of a lock system during the operations of the process sequence, the main components of the plant comprising a reversible, continuously operating scattering machine, a heatable, discontinuously operating filter press and a scattering belt box system with a rectangular scattering profile for the brown coal granules, the endless scattering belt of which system is guided in a revolving manner by two endless side steel belts through a pressure chamber, which can be sealed in a gastight manner, in the press, and it being possible to close and open the pressure chamber, transversely to the direction of transportation in the entrance and exit thereof, by means of a board which can be raised and lowered and a blocking slide gate.
Since it is necessary, for large power-plant outputs, for example for one Gigawatt power-plant output, to use a plurality of press lines each having a raw brown coal throughput in the feed region of about 200 tonnes per hour and the drying operation in each case takes place within a cycle of about 10 minutes, this amount has to be introduced into the pressure chamber via the scattering machines intermittently six times per hour, that is to say 33 tonnes per feed operation. That means, for a bulk density of about 600 kg/m.sup.3, about 55 m.sup.3 of granulated raw brown coal have to be transported into the pressure chamber uniformly with a rectangular scattering profile at a transport speed of about 0.5 m per second within a time of about 70 seconds. The problem therefore resides in controlling the volumetric flow of about 0.8 to 1 m.sup.3 per second in a uniform scattering height in discontinuous operation. This problem cannot be easily mastered using a continuous scattering and a reversible scattering machine above a fixed scattering and feed belt. The length which is required for the scattering and feed belt and the space required for this also have a disadvantageous effect on the costs of the plant.